1. Field of the Invention
This invention relates to a method and apparatus for making organic compound particles and, subsequently, atomizing those particles. The invention is disclosed in the context of a method and apparatus for atomizing chlorpropham, a compound widely used in the agricultural industry to inhibit sprouting of stored tubers.
2. Description of Related Art
It is often desirable to store certain agricultural produce until a sale under favorable economic terms can be consummated and the produce delivered to the purchaser. During storage, it is essential that freshness of the produce be maintained. Tubers, such as potatoes, are frequently stored as bulk piles in quantities of 2,270,000 to over 22,700,000 kilograms (5,000,000 to over 50,000,000 U.S. lbs.) in dark, underground storage cellars where the temperature is maintained within a range of about 4.5xc2x0 C. to 12.8xc2x0 C. (approximately 40 to 55xc2x0 F.). Untreated tubers will generally sprout over time, even in the absence of light. If the sprouting is allowed to continue unchecked, the tubers become commercially worthless. Isopropyl-3-chlorocarbonilate, an organic compound commonly known as CIPC or chlorpropham and marketed under a variety of trade names, is currently the only registered post-harvest sprout inhibitor used in potato storages in the United States. Used also as an herbicide, Its use as a potato sprout inhibitor was first reported by P. C. Marth in 1952, and its use for that purpose was later patented by the Pittsburgh Plate and Glass Co. The molecular structure of CIPC is depicted in FIG. 1. CIPC has a molecular weight of 213.66, a melting point of about 41xc2x0 C., a vaporization temperature of about 246xc2x0 C., and a vapor flash point of about 427xc2x0 C.
CIPC inhibits potato sprout development by interfering with spindle formation during cell division. Cell division is extremely important during the wound healing or curing period after potatoes are placed into storage. Wound healing requires the production of two to five new cell layers formed by cell division. If CIPC is applied to the potatoes before the wound healing process is complete, excessive losses due to tuber dehydration and disease can occur. CIPC may be applied any time after the wound healing process is complete but before the tubers break dormancy in early spring. It is not recommended to store In order to suppress the sprouting of a tuber, the tuber must be covered with a thin film of chloroprofam. CIPC is applied to the tubers as an aerosol or as an emulsifiable concentrate. The emulsifiable concentrate is generally applied to the potatoes as a direct spray during the fresh packing operation. CIPC aerosols are generally applied to potatoes in bulk storage.
Several methods have been developed for applying CIPC aerosols to potatoes in bulk storage. U.S. Pat. No. 4,226,179 to Sheldon, III et al. discloses a process whereby CIPC, either without solvent or with a relatively small amount of solvent, is atomized at a temperature of less than 121xc2x0 C. The aerosol is formed in a fogger having a cylindrical mist chamber in which ultrasonic resonance nozzles atomize the chemical agent. A tangentially introduced air flow and a helical baffle plate in the mist chamber cause centrifugal separation, leaving smaller particles near the center of the mist chamber. These small particles are carried by an airflow duct to a storage chamber containing potatoes. The aerosol condenses on the potatoes, thereby forming a growth is inhibiting film thereon. U.S. Pat. No. 5,723,184 to Yamamoto discloses a process whereby CIPC is heated to a molten state, pressurized, further heated and introduced into a heated airstream that is ducted to a storage chamber containing potatoes. U.S. Pat. No. 5,935,660 to Forsythe, et al. discloses a process similar to that of Yamamoto whereby solid CIPC is melted and then converted to an aerosol either by a pressurized hot air stream or by a combustion gas stream.
There are several drawbacks to the aerosol formation processes which inject molten CIPC into a heated airstream. The first is that of CIPC solidifying within the transport or injector lines. If an aerosol generation system having molten CIPC within the transport or injector lines is allowed to cool, the CIPC will solidify, making further operation of the equipment impossible until the CIPC returns to its molten state. In order to effectively deal with this operational quirk, molten CIPC must be removed from the transport lines when the equipment is shut down. This is typically done by replacing the molten CIPC with a solvent. Nozzle clogging can also be a problem with this type of equipment. If movement of the heated liquid CIPC is relied on to maintain the temperature of fluid transport lines removed from a primary heat source, nozzle clogging will result in solidification of CIPC within the transport lines within a short time. For this reason, liquid transport lines must also be heated. A second drawback related to the use of melted CIPC is the risk of scalding and burns to equipment operators, whether it be from the leakage of the scaldingly hot liquid CIPC from the liquid transport lines, or the need to repair application equipment containing melted CIPC. Though the maintenance risk may be minimized by allowing the equipment is to cool to safer, lower temperatures, the CIPC in the liquid transport lines will solidify at those safer temperatures, thereby hampering efforts to restart the aerosol generation process. A third drawback to the use of melted CIPC for the generation of aerosols is that of equipment warm up time. The equipment and the solid CIPC act as a heat sink, which must be raised to operational temperatures for the aerosol generation process to function properly.
What is needed is a new CIPC aerosol generation process which does not require the conversion of solid CIPC to a liquid which must be contained by the aerosol generating equipment prior to its conversion to an aerosol.
The present invention provides both a method and multiple apparatus for atomizing chlorpropham (CIPC) or any other similar organic compound which does not require the conversion of solid CIPC to a liquid which must be contained and transported by the aerosol generating equipment prior to its conversion to an aerosol. The process includes the steps of forming minute particles of solid CIPC particles from a larger block or chunks of solid CIPC, and inducting the particles into an airstream wherein the particles are provided with sufficient thermal energy to convert them into an aerosol. The process may be implemented by abrading a block of solid CIPC with a wire brush, by shaving a block of solid CIPC with a blade, or by pulverizing chunks of solid CIPC to convert it to a powder. Pulverization may be accomplished, for example, by placing the chunks in a chamber having a spinning blade. A common food blender on a high-speed setting will produce CIPC powder having a consistency similar to that of talcum powder. For a first embodiment of the invention, the block of solid CIPC is slidably inserted within a chute that connects with a cylindrically shaped housing. The brush, also cylindrically shaped, revolves about its axis, which coincides with that of the housing. Particles abraded by the brush are drawn by differential air pressure through a slot at the base of the housing into an intake manifold having a moving air stream. The air stream is motivated by the propeller of a turbine, to which the manifold is coupled. The impeller inlet of the turbine is coupled to a source of compressed air. The turbine propeller, which is spun at speeds comparable to those achieved by an automotive turbocharger, also pulverizes the abraded particles. From the turbine propeller outlet, the air stream is routed to a heated chamber which, preferably, contains a series of baffles which repeatedly deflect and heat the airstream. The pulverized CIPC particles are converted to an aerosol within the heated chamber. The process has been used to convert solid CIPC to an aerosol at the rate of more than 20 kg per hour. Once conversion to an aerosol is complete, the airstream is directed to a potato storage facility and allowed to bathe tubers stored therein. In the case where CIPC particles are shaved from a solid block, the particles may be passed through rapidly spinning blades, which pulverize the particles into CIPC dust. The blades are preferably spun with an air-powered motor or, alternatively, with an electric motor. In the case where the CIPC is pulverized to dust and subsequently loaded in a hopper from which it is fed to a heated air stream, the particles are sufficiently small as to require no further treatment prior to heating. One consideration is that a mass of pulverized CIPC particles tend to agglomerate with time. Therefore, it may be desirable to stir the particles continually, or at least periodically, in order to slow the agglomeration process. Agglomeration may also be slowed by cooling the pulverized mass of CIPC particles. However, cooled particles require more heat input to convert them to an aerosol. The pulverized CIPC particles may be fed from the hopper into the airstream via a wire-brush auger. Continual vibration to the mass of pulverized particles to prevent bridging of the particles within the hopper that would interfere with the entry of particles into the auger intake port.